Early venetian blinds were made with wide flat wood slats, but presented some problems because of warping, breakage and deterioration of the surface finish. Venetian blinds were later formed with slats of thin transversely arcuate sheet metal stock and, more recently, venetian blind slats have been formed of solid plastic material by thermo forming strip plastic sheet material or by extrusion.
U.S. Pat. No. 4,711,005 discloses thermo forming venetian blind slats from PVC strip material. As disclosed in that patent, thin PVC strip 2.5 cm in width and 0.05 to 0.06 cm in thickness is thermo formed to a shallowly curved 7.62 to 12.7 cm or greater radius in curvature. However, solid plastic materials such as rigid polyvinyl chloride commonly used in the formation of plastic venetian blind slats, have a density that is three or four times higher than the density of the woods used in wooden slats, and it was necessary to reduce the thickness of the solid plastic slats to control the lift weight of the blind, and to also reduce the spacing of the ladder tapes in order to prevent sagging or drooping of the plastic slats under the temperature and humidity conditions sometimes encountered in window areas.
U.S. Pat. No. 4,818,590 discloses forming wood veneer covered structural rigid plastic foam elements including venetian blind slats, having a rigid plastic foam substrate and a wood veneer adhered to opposite surfaces of the substrate. U.S. Pat. No. 5,121,785 discloses forming a venetian blind slat using a metal core plate with a wood veneer adhered to opposite faces of the metal core plate, and synthetic resin layers overlying the wood layers. In one alternative construction, a fiber reinforced plastic is substituted for the metal core plate, and in still another embodiment, the slat is formed with a wooden core plate with reinforcements of non-woven fabrics and resin sheets mounted to both faces of the core plate, and a pair of wooden plates mounted to the faces of the reinforcements. The formation and laminating of the slats from multiple individual layers as disclosed in these patents, necessarily increases the overall cost of making such venetian blind slats.